Art of permanently heat-expanding cast-iron articles.



guna tot lllllunlilllllalinlil-J Patented Aug. 6, 19m` Ummm 0 APPucATlou min ocr. z's. ma.

W. A. KNAPP. ABT 0F PEBMAN-ENTLY HEAT XPANDING CAST IRON ARTICLES.

To all-'whom t may concern WILLIAM A. K N'APP, 0F WASHINGTON, DISTRICT 0F COLUMBIA, ASSIGNOR, BY DIRECT AND MESNE ASSIGNMENTS, TO CHARLES SCHWARTZ, TRUSTEE, OFiWASHINGjTON,

`DIS'JIBJCT 0F COLUMBIA.

Be it known that I, WILLIAM A. KNArP,

'la citizen of the United, Statesresiding at Washington, District of Columbia, have invented certain new and useful Improvements :in the Art of Permanently Heat-Expanding Cast-'Iron Articles, of which the following is a specification. f I

My invention relates to a process of treating inished cast iron articles by which they are permanently heat-expanded, and consists of the process .herein to lbe described and to the products of such rocess.

y I have discovered t at iron castings, when 'subjected to a red heat and then allowed to cool slowly, may become lpermanently expanded, that is tosay, they do not, upon cooling, contract to the same. sizes as they had before being heated, but remain permanently enlarged to` a perceptible degree.

' I believe that this is true of all kinds of iron castings, but the ltendency to expand permanentlyfis particularly pronounced in hollow castings, and more especially in thoseof cylindrical form, such as gas engine pistons. Furthermore, 'I have also discovered that castings so expanded may be again pervmanently expanded and the' process repeated until a substantial degree of enlargement is secured.

I have applied my invention practically to Y the expansion and retting of worn or loose cast iron 'engine pistons, particularly tothe pistons -of gas engines, and more especially to those of engines used upon motor vehicles;

'and I shall in this application describe the process in connection with the expanding of and refitting of such pistons,4 although the principle of the invention 'may be applied to advantage to the tting of new pistons and cylinders, and to the expandingl and litting of other articles` than pistons.

In the accompanyingdrawingsd Figure 1 is a longitudinalsectional View through the cylinder of an internal combus` tion engine, whichhas been used untilthe cylinder has become so worn that the piston no longer lits it accurately and tightly, the view being lar ely diagrammatic in its character, and the iowing of the extent to which the cylinder is worn exaggerated;

Fig. 2 is a view illustrating one method of heating a piston to expand it; and

' Specification of Letters Patent.

original application med october 7, 1915,

r on PEBMANENTLY nnarpnxr-IANDING cesar-mori ARTICLES;

.Patented Aug. 6, 1918. l

Serial No. 54,613. Divided and this application led October 28, 1915.r Seria1N0.58,44.

Fig. .8 is an elevation illustrative of the heat-insulating material, such as asbestos, c l

a yhot bed, as of glowing charcoal, upon which the incased piston is seated, and d a blow torch delivering flame into the interior of the piston for heating it. The illustration in Fig. 2 is typical, though practical and one'that has been employed byme.

When the article being heated has been `raised to the desired temperature the appliy cation of heat is discontinued and the casting allowed to cool slowly. This maybe accomplished by removing'the torch and covering sheet of asbestos, such as indicated at e in Fig.L 3. The jacket b land covering e ynot only .insure a gradual and uniform cooling, but largely loperate toprevent access of air to the aticle a, thus reducing the liability of resultjthat the'casting'will be again, and

further, enlarged, the second expansion being also permanent, and this alternate heatv ing and cooling may be carried on with safety alnumber of times so as to secure e considerable enlargement of-the article.

'76 the open end of the piston, as by means of a p One extremely useful and valuable application of my invention is to the reitting of pistons to' engine cylinders where one or both have become worn. I refer to Fig. 1

ofthe drawings where a; indicatesthe piston of a gas engine, and f the cylinder in which it works, these, particularly the cylinder, having become, through use, so worn that the piston no longer fits the cylinder tightly.

4 In practice the piston of a gas engine'becomes somewhat reduced in diameter through wear, and the cylinder in which it Works' becomes enlarged, particularly at those parts opposite which the piston travels, as indicated at g in Fig. l, so that the cylinder chamber becomes larger at the rear parts g than at the front portion ha. When this occurs it is now the common practice to obtain a new, oversize piston, and to rebore the cylinder to fit such piston. rifhis practice is expensive and not. always satisfactory, as the reboring is often attempted upon a machine not especially intended for that purpose, with the result that the engine cylinders are frequently seriously injured. Furthermore, the balance of the engine by the use of an oversize piston is disturbed, and this is believed by some to injuriously ailect the running of an engine thus equipped.

By the use of my invention l am enabled to overcome the objections tothe use of an oversize piston replacing one that has become worn, to materiallyv reduce the expense incident to the installation of such a. piston,

land to insure a uniformly better result. To

secure this l expand the worn piston, according to the method already herein described, until it lits closely the outer portion li of the cylinder. l then insert this expanded piston into the open end of the cylinder, and grind the lat-ter, by means, for instance, of the piston, using someabrasive between them, taking ofi' the high places and irregularities of the cylinder and bringing it ,to true cylindrical shape and to a slightly greater diameter than it originally had. lf a single grinding be not sufficient the piston is a second time expanded and the grinding and shaping process just. described repeated, and this is continued until the cylinder throughout its working portion is brought to true cylindrical shape and of the desired diameter to lit the piston. 'Iiwo or three alternate expanding and grinding operations have been usually found to be sufficient to restore a considerably Worn cylinder to good working condition. Should the expansion of the piston at any time be found too great to permit of its insertion into the end Il, of the cylinder, it may be reduced in diameter by turning. Not only is the process useful in relitting old pistons to old cylinders, but itV will be found of advantage in obtaining a perfect lit between new cylinders and new pistons.

'lt is wellJ understood that a better lit is obtained by grinding two parts together than where it is sought to secure the desired result by turning processes alone, and by my process the fitting, by the grinding together of cylinder and piston, is easily made practically possible.

lhe temperatures to which the articles being treated according to my process are Lafrance heated, hereinbefore mentioned, that is, between 1400 and 1600 degrees F. are those that ll have found the most practical under ordinary conditions, but they do not mark the limits ofthe temperatures between which my invention may be worked, because .ll have found that a temperature as low as about 12000 F. will cause a slight permanent expansion of an article subjected to that heat and treated according to the process herein described, and such relatively low temperature, or one between that and 14000 F. may be 4to advantage employed where a very slight expansion is desired.. lll'hile l am not now able to fix the limits of temperature for heating the articles when practicing my process, with accuracy, l believe that the term red heat describes with approximate accuracy the range of temperatures available for the heating step of the process.

l am aware that for sometime has been ylrncvvn the fact that cast iron articles when heated to av temperature of about 900 to 12000 F. and then allowed to cool become Sti permanently expanded, this fact having been .noticed in connection with a method of operating upon chilled iron castings, such as car wheels, for the purposeof increasing the strength of the metal and relieving the castings from those undesirable strains to which they fare subjected by reason of the chilling process. However, so far as li am aware, this property of cast iron to become 4permanently expanded under certain condithis l am not informed, this is and has been a negligible factor, and one hitherto quite or almost entirely overlooked and unknown.

@n the other hand, in the practice of my invention, the change in the size of the article, due to the heat treatment to which it is subjected, is the object sought, and any change in its physical or molecular condition, due to such treatment, is incidental, and negligible. llt is common practice in annealing to subject the articles to a heat treatment for a comparatively long time, and to give them one treatment only; whereas in the practice of my invention l have found that it is not necessary that the heat treat-ment should be long continued, it being onl necessary to uniformly heat the article t roughout and bring it up to a red color, immediately after which it is allowed to cool. Moreover, ac-

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newness cording to my process, the heat treatment of a particular article may be, and in practice often is, repeated to get successive expansions and added enlargements of the article, the desired increase in size being thus obtained through a stepping-up process. In operating upon comparatively' small articles, such as the pistons of gas engines Where the volume of metal in each is ,not large, the length of time required to heat the article to the necessary de ee is short; and as herein pointed out, if t e temperature be raised only to approximately 1200", a very, slight lenlargement takes place. Thus by heat treatment alone an exceedingly accurate t of a cast iron article to the space it is to occupy, or to another article With which it is to be used, may be quickly and cheaply secured,

lthe successive treatments permitting it to be gradually brought up to the deslred size.

This case is a division of my application No. 54,613, filed October 7 1915.

NVhat I claim is 1. The herein described improvement in the art of permanently heat-expanding cast iron which consists in heating the metal to a red heat and then, immediately after the metal has been uniformly heated to the desired degree, uniformly cooling it.

2. The herein described process of causv ing the permanent'expansion of iron castings Which consists in bringing them to a red heat, then after the castings have been brought to the desired degree of heat, immediately allowing them to Icool, and alternately repeating the said heating and cooling steps to successively expand the articles to the desireddegree.

3. The herein described improvement in the art of tting cast iron pistons to cylinders in which they Work, which consists in permanently expanding a finished piston to the desired size by subyecting such piston to permanently heat-expanding*- 'the piston' nearly to the desired size by heating it to a red color uniformly throughout and then cooling it, and then subjecting it to a further permanent heat expansion by which it is brought to the desired Working size.

5. The herein described process of causing the permanent expansion of an iron casting which consists in heating the casting uniormly throughout to a temperature between 1400 and 1600 degrees F. and then inlinediately after such uniform heating has been .attained cooling the article.

, WILLIAM A. KNAPP. 

